Dogon People -- Precession of the Equinoxes and the Sirius Cycle

Dogon People -- Precession of the Equinoxes and the Sirius Cycle

What Precession Is

The Earth's rotational axis slowly traces a circle over approximately 25,772 years -- a wobble caused by the gravitational pull of the Moon and Sun on Earth's equatorial bulge. This slow rotation of the axis means that the position of the celestial poles changes over millennia: in 2500 BC, the North Pole pointed toward the star Thuban; today it points toward Polaris; in 14,000 CE it will point toward Vega.

Precession also means that the position of the Sun at the equinoxes and solstices, relative to the background stars, shifts gradually. The Sun at the spring equinox currently occupies the constellation Pisces; approximately 2,000 years ago it was in Aries (giving us "the Age of Aries"); it is slowly moving toward Aquarius.

Precession and the Sothic Cycle

The Egyptian Sothic cycle -- based on the annual heliacal rising of Sirius -- is related to precession through the relationship between the tropical year (the solar year based on the equinoxes, affected by precession) and the sidereal year (the year based on the stars' positions, not affected by precession). The Sothic cycle of approximately 1,461 years represents the accumulated difference between these two year lengths at the latitude of ancient Egypt.

Sirius's heliacal rising -- its annual appearance before sunrise after 70 days of invisibility -- slowly changes its calendar date due to precession. Over thousands of years, the heliacal rising drifts through the calendar. For ancient Egyptians observing Sirius's rising over centuries and millennia, the precession would be a known and tracked phenomenon.

Can Precession Explain the Dogon's Sirius Knowledge?

Some researchers have proposed that the Dogon's deep familiarity with Sirius -- including potentially the detection of its binary nature -- could be a consequence of their multi-generational dedicated observation of the star's position, brightness, and behaviour.

The argument runs:

• Long-term observation of Sirius might reveal subtle variations in its apparent brightness or position caused by the gravitational interaction with Sirius B
• If ancient Dogon astronomers tracked Sirius over many generations, they might have noticed a ~50-year periodicity in some observable property
• This periodicity could then be encoded in the cosmological system as a 50-year orbital period for an invisible companion

The problem with this argument: the gravitational wobble Bessel detected in Sirius A's proper motion in 1844 required the precision of a mid-19th century German telescope and the mathematical sophistication to calculate a companion's orbit from the data. Naked-eye observation of Sirius would not reveal this wobble. Sirius B produces no visible brightening or dimming of Sirius A detectable by human senses.

Precession observation is plausible as an explanation for the Dogon's general astronomical sophistication. It cannot explain the specific claimed knowledge of Sirius B's orbital period, density, or invisibility.